Judges of the state's highest court grilled the lawyer for a woman who killed her infant daughter, asking yesterday why that slaying should not override the presumption that the mother, Latrena D. Pixley, is the best person to care for the son she bore after the killing.

The boy's foster mother, who wants permanent custody of Cornilous, is asking the Court of Appeals to overturn a Montgomery County circuit judge's ruling that would return the child to his mother.

Four of the seven judges asked Jennifer Evans, Pixley's lawyer, why infanticide should not be considered an extraordinary circumstance that could negate the presumption in Maryland law that a child is better off with a biological parent or why state law should not be read to deny custody to someone who has abused another child.

"I want to know what an exceptional circumstance would be if you don't consider murder of a child an exceptional circumstance?" said Judge John C. Eldridge.

Evans said there are several factors to be considered, such as the age of the child and the length of time the child has been away from the parent.

"You don't want to answer my question," Eldridge replied.

Pixley, 24, was convicted of the 1992 murder of her 6-week-old daughter in Washington but given a light sentence when a District of Columbia judge agreed that she was suffering from post-partum depression. She was jailed again in 1996, three months after giving birth to Cornilous, for violating her probation by committing credit card fraud.

Cornilous, 2, has lived with Laura P. Blankman, 28, a Montgomery County police officer, since then. Pixley, who is on probation again, moved this year to a supervised home for troubled women where Cornilous can visit her overnight.

Montgomery County Circuit Judge Michael Mason ruled in December 1997 that Cornilous would be better off with Pixley, and the Court of Special Appeals upheld that decision in July, leading to yesterday's arguments.

"I was very encouraged," said William Pierce, president of the National Committee for Adoption, one of 11 advocacy groups that filed a friend of the court brief backing Blankman.

"It seemed like we were on the short end," said Ralph E. Hall Jr., one of Pixley's lawyers.

Lawyers on both sides have asked the court to expedite a ruling for the benefit of the child. They cautioned against reading too much into the judges' questions.

In an unusual request, lawyers for Blankman and Cornilous asked the high court to substitute its judgment for that of Mason, rule that murder removes the presumption that a child is better off with a biological parent and award the child to Blankman.

The court's other options are to affirm the lower courts or return the case to Mason for reconsideration based on certain points of law.

Outside the court, Pixley's lawyers said she is a different person from the despondent 19-year-old who snapped as her baby cried in hunger. She is a receptionist, attends the University of the District of Columbia and remains in therapy and counseling. She has two other grade-school sons, one living with relatives and one in foster care, and she has not been accused of abusing or neglecting them.

The judges questioned lawyers on fine points of the state's family law. Pixley's lawyer argued that it refers to returning an abused child to the abuser.